1. Field of the Invention
The present invention relates to a structure of a blade for a fan which is generally used to deliver cooling air or the like in automotive engines or various other kinds of apparatus.
2. Description of the Prior Art
A typical conventional variable-pitch type fan blade is exemplarily shown in FIGS. 5 and 6. As illustrated, blades 12 are provided on a boss member 11 so as to project outward from the outer peripheral surface of the latter, and a bimetal 15 is provided substantially all over the deliveryside surface of each blade 12 so that, as the temperature of the air delivered by the fan rises, the bimetal 15 is deformed to increase the quantity of camber C of the blade 12, thereby increasing the quantity of air delivered when the air temperature is relatively high, whereas, when the temperature of the air delivered is relatively low, the camber quantity C is reduced to decrease the quantity of air delivered, thus reducing the fan driving power and the fan noise.
The above-described prior art fan blade structure suffers, however, from the following problems. The deformation of the blade 12 caused by the deformation of the bimetal 15 that takes place in accordance with a change in temperature of the air delivered mainly changes the camber quantity C but causes substantially no change in the angle of attack .alpha., as shown in FIG. 7. Accordingly, it is impossible, with an increase in the camber quantity C alone, to obtain a substantial increase in the quantity of air delivered, and therefore the expected object cannot be attained. For this reason, it is necessary to employ a temperature-sensitive fan clutch, which results in complication of the control mechanism, an increase in the overall size of the apparatus, and also an increase in the weight of the product.